1. Field of the Invention
The present invention relates to a driving apparatus for moving a moving member using a belt and a drive pulley.
2. Description of the Related Art
A driving apparatus for moving a moving member by a belt and a drive pulley is used in a mechanism for moving a carriage of a recording apparatus. The driving apparatus is described below using a recording apparatus as an example.
In the recording apparatus using an ink jet recording method, a carriage with a recording head mounted thereon scans over a recording material and, concurrently with the scanning operation, the recording head is driven to perform a recording operation. To obtain a high definition output image with the above-described ink jet recording apparatus, many recording apparatuses employ a direct current (DC) motor as a drive source for driving the carriage and further employ a servo control for feeding back position detection information to the recording apparatus by a linear encoder. Such a configuration can realize highly-precise position control and a high-speed stable scanning operation. In addition a method is used in which driving of the recording head is controlled according to a detection timing of the linear encoder and a timing between the scanning operation of the carriage and the driving of the recording head can be precisely adjusted.
A toothed (timing) belt excellent in a cost-effectiveness, easy assembly, an d precision, is used as a mechanism for conveying a scanning/driving force to the carriage from the direct-current (DC) motor functioning as a drive source. The toothed (timing) belt is stretched between a drive pulley driven by the DC motor and an idler pulley with a predetermined tensile force and teeth notched around the drive pulley mesh with teeth provided on the toothed belt, and the driving force is transmitted. The carriage with a recording head mounted thereon is coupled with the toothed belt to reciprocate between both pulleys according to rotation of the DC motor.
The carriage performs an abutment operation against a housing, such as a chassis, for the purposes of initialization of a position in a scanning direction and a relative movement of a mechanism unit provided within the carriage. At this time, the abutment operation may be executed by pulling the carriage in a direction approaching to the idler pulley by the toothed belt. However, the idler pulley is suspended via a tension spring, so that the idler pulley is slightly moved by being pulled toward to a side of the drive pulley at a moment when the carriage abuts against the chassis and stops. During the abutment operation of the carriage, the drive pulley keeps rotating by the DC motor. Therefore, the toothed belt is warped between the carriage due to an excessive portion of the toothed belt resulting from decrease of a distance between the idler pulley and the drive pulley. Since the drive pulley further keeps rotating, idling of the drive pulley occurs with respect to the toothed belt.
In a case where the carriage is left for a long time without performing scan, a sliding friction of the carriage may become larger due to a stain of ink or the like firmly stuck on a guide for guiding the carriage. In such a case, an issue of the idling of the drive pulley also occurs similar to the abutment operation.
A configuration including a member for preventing the toothed belt from jumping (i.e., a tooth jumping) in the vicinity of the drive pulley of the toothed belt coupled with the carriage as discussed in Japanese Patent No. 3805155 is known in order to solve the above issue.
A cost and a size tend to increase in the above-described ink jet recording apparatus. Recently, in order to decrease vibration when the drive pulley meshes with the belt, a high accuracy belt with a fine tooth pitch and a low tooth height has been employed in some cases. In the above-described case, a gap between the member for preventing the jumping and a back surface of the belt is required to be narrowed as much as possible. However, friction may occur between the member and the back surface of the belt depending on an assembled condition. The vibration caused by the friction cancels out an effect of vibration reduction produced by lowering the tooth height. In addition, the belt may be damaged or broken due to the friction or the vibration.
On the other hand, to prevent the drive pulley from the idling thereof, it is effective to increase a tensile force of the toothed belt and enlarge and/or heighten the teeth of the toothed belt. However, the increase of the tensile force of the toothed belt may increase a drive load. Therefore, a large capacity motor is required to be installed, which, however, causes an increase in the cost and the size of the apparatus. In addition, a toothed belt having higher teeth may vibrate when the teeth thereof mesh with the teeth of the drive pulley. As a result thereof, a scanning speed of the carriage may become uneven.